CA2134330A1

CA2134330A1 - Process for stabilising copolymers of maleic anhydride and vinyl ethers

Info

Publication number: CA2134330A1
Application number: CA002134330A
Authority: CA
Inventors: Harald Meyer; Axel Sanner; Franz Frosch; Hans Richter
Original assignee: Individual
Current assignee: BASF SE
Priority date: 1992-04-29
Filing date: 1993-04-20
Publication date: 1993-10-30
Also published as: WO1993022374A1; JP3264927B2; ES2096294T3; JPH07506136A; EP0638105A1; US6008274A; DE59305271D1; EP0638105B1; DE4213972A1

Abstract

Abstract of the Disclosure: A process for stabilizing a copolymer of maleic acid or maleic anhydride and vinyl alkyl ethers against a reduction in molecular weight in aqueous solution or in the solution of an organic solvent by adding 0.001 to 10 % by weight, based on the copolymer, of a reducing agent, a tert-butyl-containing phenol or a mixture thereof.

Description

213~330 O.Z. 0050/43~87 Stabilization of co~olvmers of maleic acid or maleic anhYdride and vin~l alk~l ethers The pre~ent invention rslates to a proce~s for stabilizing copolymers of maleic acid or ~aleic anhydride and vinyl al~yl ethers against a reduction in molecular weight in aqueous solution or in an organic solvent.
Copolymers of maloic acid and v~nyl alkyl ether~
or copolymers o maleic a~hydride and vinyl alkyl ethers are known substancQs, cf. US-A-2,047,398 and Ind. Eng.
10 Chem., Volume 41, pags 1509 (1949). Copolymer~ of maleic anhydride and vinyl alkyl ethors are hydrolyzsd on diasolution in w~ter, one anhydride group forming two carboxyl group~. Tho copolymers are then formally built up from maleic acid and vi~yl alkyl ether units. The vi~cosity of the agueous solution~ of copolymers of maleic acid and vinyl al~yl ethor~ is a logarithmic function of the molecular woight. According to Technical I Bulletin 7543-017 published ~y GAF Corporation in 1965, the maximum handleable concontrations of copolymsr~ of maleic acid and alkyl vinyl ethers at 25C ~or a polymsr having a ~pecific visco~ity (1 g per 100 ml of methyl ethyl ketone) of from 2.6 to 3.5 i~ 20 % by weight and for copolymor~ having a ~pacific vi~co~ity of from 0.1 to 0.5 is 35 % by we~ght. At th-~e relatively low polym~r concentrations, in partlcular the high-viscosity and dilute aqyeous solutions or solutions of copolymers of mal~ic acid ~nd alkyl vinyl ethers are su~ceptible to a reduction in the molecular weight (cf. B.C. Trivedi and B.M. Culbertson, Maleic Anhydride, Plenum Press, 30 New York, 1982, p. 437.
US-A-2,789,099 disclo~es that agueou~ solution~
of polyacrylic acid can be stabilized against gelling during atorage by polymerizing acrylic acid in aqueou~
~olution in the pre~ence of sodium hypophosphite as visco~ity regulator and in the pre~ence of copper ~alt~.

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- 2 - O.Z. 0050/43187 DE-A-3,030,344 disclo~es that pulverulent, high-molecular-weight acrylamide polymer~ can be prepared by drying aqueous ~olutions of thsse polymers in the presence of tert-butyl-containing phenols, thioether~ or 5 phosphites. These compound2 may al~o be present as early as during the polymerization. They prevent the polymer~
becoming i~sol~ble during drying.
It i~ an object of the prqsent invention to stabilize cGpolymQrs of maleic acid ox maleic anhydride 10 and alkyl vinyl ether~ against a reduction in molecular weight, which occur~ in particular in aqueous solution or in an organic solvent.
WQ have found that this object is achieved by a process for stabilizing a copolymer of maleic acid or 15 maleic anhydride and vinyl alkyl ethers again~t a reduc-tion in molecular weight, which compri~es adding from 0.001 to 10 % by weight, based on the copolymer, of a reducing agent, ~elected from the group consisting of sulfurous ac~d, phosphinic acid, dithionic acid, a~corbic 20 acid and ammonium or alkali metal ~alts of said acids, to a solution of the copolymer in water or an organic solvent.
Suitable reducing agents are all compounds which have a reducing action, for example sulfurous acid, 25 dithionic acid, hydrogen sulfide, hypophoephorous acid, phosphinic a~:id, phosphorous acid, diphosphoric acid, hypophosphoric acid and the water-~oluble ammonium, alkali metal and alkaline earth metal salts of said acid~. Preferred reducing agents are sulfurous acid, 30 phosphinic acid, dithionic acid and ascorbic acid, either as a free acid or in the form of ammonium or alkali metal salts.
; The copolymers are ~tabilized by adding the ', suit3ble stabilizers to solution~ of the copolymers in ; 35 water or an organic solvent. The stabilizers are employed in amounts of from 0.001 to 10 % by weight, preferably J from 0.01 to 5 % by weight, usually in amounts of from 0.05 to 2 % by weight. They can be added to the copolymer AM~NDED S~EET
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-' S' ' , ' ~. . ' 21 3~330 - 3 - O.Z. 0050/43187 501ution8 directly after the polymerization or to polymer solutions if they are to be stabilized against a xedue-tion in molecular weight. The stabilizers are u~ually added-to the solution directly after the polymerizaticn 5 R0 that a reduction in molecular weight i~ prevented even during work-up of the copolymers.
The copolymer~ have an essentially alternating ; ~tructure and contain maleic anhydride or maleic acid aR
one essential ~omponent and at lea~t onç alkyl vinyl ether as the other component. Any alkyl vinyl ether can be ueed here for the preparation of the copolymer~, for example vinyl alkyl ethers having 1 to 30 carbon atoms in the alkyl group. Preference i~ given to vinyl alkyl ether~ which have 1 to 18 carbon atoms. The use of stabilizer~ iR of particular interest in the ca3e of copolymer~ of high molecular weight. For example, the Fikentscher R values for copolymers of maleic anhydride and alkyl vinyl ethers is from 25 to 110, measured in 1 %
strength by weight ~olution in cyclohexanone. Copolymer~
having R value~ of greator than 45 are preferably ~tabilized according to the in~ention.
Copolymers of maleic acid and alkyl vinyl ether~
have R values of from 30 to 180 (determined on the eodium salt by the Fikont~cher method at a polymor concentration 25 of 1 % by wei.ght and at 25C and pH 7) or from 30 to 330 (determined by the Fikentscher method at a polymer , concentration of 0.1 % by weight and at 25C and pH 2).
¦ While low-molecular-weight copolymer~ of maleic anhydride or maleic ac:id and alkyl vinyl ethers are relatively stable, even in ~olution, solutions of relatively high-molecular-weight copoly~ers rapidly undergo ~"

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- 4 - 0.~. 0050~43137 undesired degradation if the copolymers are not stabilized. The stabilizers are expediently added to the solutions of the copolymers at from 0 to 60C, preferably at from 10 to 45C. Suitable ~olvent~ for copolymer~ of maleic anhydride and alkyl vinyl ethers are all organic solvent~ which do not react with the anhydride group~ of the copolymer, for example ketone~, e~ter~ and ethers.
Examples of individual compound~ are acetona, methyl ethyl ketone, ethyl acetate, i~opropyl acetate, butyl acetate, iQobutyl acetat0, tetrahydrofuran, methyl acetate, butyl formate, cyclohexano~e, cyclopentenone and propyl formate.
The concentration of the copolymers in the organic solvents i8 uBually fro~ 5 to 70 % by weight.
; 15 Copolymers of maleic acid and vinyl alkyl ethers~ are preferably stabilized in the form of aqueo~
solutions.
The R value~ indicated in the exa~ple~ were determined by the m~thod of H. Fikentscher, Cellulosechemie, Volume 13 (1932), page~ 58 to 64 and 71 to 74. Copolymers of maleic anhydride and al~yl vinyl ethers were determined in 1 % strength solution in cyclohexanon~ and copolymers of maleic acid and alkyl vinyl ethor~ were determlned in 0.1 % strength aqueous solution, in both case~ at 25C and pH 2.
i EXAMPLES

Preparation of the copolymers Copolymer 1 155 g of acetone were introduced under nitrogen into a 2 1 gla88 flask fit~ed wlth anchor 3tirrer, re$1ux condenser and metering devices. A solution of 300 g of maleic anhydride in 400 g of acetone ~erved as feed 1.
;l 264 ml of vinyl methyl eth~r served as feed 2. A solution of 4.5 g of 2,2'-azobi~(2,4-dimothylvaleronitrile) in 90 g of acetone formed feed 3. 45 ml of fsed 1, 15 ml of ~ feed 2 and 15 ml of feed 3 were introduced into the ,~
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2~3~330 - 5 - o.Z. 0050/43187 fla~k, and the mixture was then heated to the boil. After 15 minutes, feed 1 and feed 2 were metered in over the course of 4 hours and feed 3 over the cour~e o~ 5 hours, with a con3tant reflux being maintained. WhQn the addi-5 tio~ of feed 3 was co~plete, th~ mixture wa~ poly~erizedat the bo~ling point for a ~urther 2 hours. 150 ml of acetone wa~ then removed by distillation, giving a clear, colorless solution having a solids content of 48.9 % by weight and a R value of 59.2 (1 % strength in cyclo-~' 10 hexanone).
~, 60 g of water were added to this solution at 56C
over the course of one hour, and the mixture was ~tirred at this temperature for a further hour. The solvent wa~
then removed by distillation at 800 hPa, with 1,550 g of water beiLg added in portions. In totai, about 800 ml of the solvent were distilled off. When the distillation wa~
complete, a slightly y~llowi~h solut~on having a solidG
content of 25.3 % by weight W28 obtained. The R value (0.1 % strength by weight in water at 25~ and pH 2) wa~
20 162.3 and the specific vi~cosity ~p wa~ 1.2.
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? Copolymer 2 ~ The proceduro was ~imilar to that described for A th~ preparation o$ copolymor 1, but tho polymerization lnitiator used wa~ 2.2 g of tert-amylporneodecanoate. A
clear, colorle~s ~olution having a solid~ content of 50.1 % by welght was obtained. The R valu~ of the copoly-I mer o~ mal~ic anhydrid~ and v~nyl methyl ether was 70.3 (1 % strength by weight in cyclohexanone). Hydrolysi~
gave a virtually colorless, agueous solution having a solids content of 13.4 % by weight. The copolymer of maleic acid and ~ethyl vinyl ether had a R value of 208.4 (0.1 % strength in water at 25C and pH 2).

EXAMPhE 1 1, Samples of the 25.3 % str~ngth by weight aqueous solution of copolymer 1 were introduced at 25C into colorle~ gla~s bottles, the stabilizers indicated in .,,~ .
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- 6 - O.Z. 0050/431B7 Table 1 were added, and the samples were stored at 25C.
In caae (f), the mixing and ~torage t~mperature was 45C.
For comparison, an un~tabilized sample (g) was stored together with the stabilized samples at 25C. After the time~ i~dica~ed in Table 1, the R values of the copolymers were determined. They serve as a measure of the ~foat1ve~-uu o~ the utaoil1zeru t-~t-d.

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, , ., 2134~30 - 8 - o.Z. 0050/43187 The 13.4 % ~trength by weight aqueou~ solution of copolymer 2 was dividad into a nuMber of portions, and the amounts of ~tabilizers indicated in Table 2 were added to each portion. With the exception of sample (f), in which 0.05 % by weight of phosphinic acid wa~ used as : stabilizer, 0.1 % by weight of the stabilizers indicated in Table 2 was added in each ca~e. While the temperature of ths zqueous eolution ~n Example~ a to e was 25C, it was 45C in Example f. The aqueou~ ~olution~ of copolymer . 2 stabilized in this wsy were stored at 25C (Examples a ; to e) or 45C (~xample f). After ths time~ indicated in Table 2, samplea were taken in each case, and the K
values of the polymers were determined. The reRults are shown in Table 2. For compariso~, an un~tabilized sample W~13 tontnd Ig).

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Claims

We claim:

1. A process for stabilizing a copolymer of maleic acid or maleic anhydride and vinyl alkyl ethers against a reduction in molecular weight, which comprises adding from 0.001 to 10 % by weight, based on the copolymer, of a reducing agent, selected from the group consisting of sulfurous acid, phosphinic acid, dithionic acid, ascorbic acid and ammonium or alkali metal salts of said acids, to a solution of the copolymer in water or an organic solvent.

2. A process as calimed in claim 1, wherein one of said reducing agents is added to a solution of the copolymer in water.